/*
 * Copyright 2002-2015 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package qunar.tc.bistoury.instrument.client.spring.el;

import java.lang.reflect.Array;
import java.util.*;

/**
 * Represents selection over a map or collection.
 * For example: {1,2,3,4,5,6,7,8,9,10}.?{#isEven(#this) == 'y'} returns [2, 4, 6, 8, 10]
 *
 * <p>Basically a subset of the input data is returned based on the
 * evaluation of the expression supplied as selection criteria.
 *
 * @author Andy Clement
 * @author Mark Fisher
 * @author Sam Brannen
 * @author Juergen Hoeller
 * @since 3.0
 */
class Selection extends SpelNodeImpl {

    public static final int ALL = 0; // ?[]

    public static final int FIRST = 1; // ^[]

    public static final int LAST = 2; // $[]

    private final int variant;

    private final boolean nullSafe;


    public Selection(boolean nullSafe, int variant, int pos, SpelNodeImpl expression) {
        super(pos, expression);
        Assert.notNull(expression, "Expression must not be null");
        this.nullSafe = nullSafe;
        this.variant = variant;
    }


    @Override
    public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
        return getValueRef(state).getValue();
    }

    @Override
    protected ValueRef getValueRef(ExpressionState state) throws EvaluationException {
        TypedValue op = state.getActiveContextObject();
        Object operand = op.getValue();
        SpelNodeImpl selectionCriteria = this.children[0];

        if (operand instanceof Map) {
            Map<?, ?> mapdata = (Map<?, ?>) operand;
            // TODO don't lose generic info for the new map
            Map<Object, Object> result = new HashMap<Object, Object>();
            Object lastKey = null;

            for (Map.Entry<?, ?> entry : mapdata.entrySet()) {
                try {
                    TypedValue kvPair = new TypedValue(entry);
                    state.pushActiveContextObject(kvPair);
                    state.enterScope();
                    Object val = selectionCriteria.getValueInternal(state).getValue();
                    if (val instanceof Boolean) {
                        if ((Boolean) val) {
                            if (this.variant == FIRST) {
                                result.put(entry.getKey(), entry.getValue());
                                return new ValueRef.TypedValueHolderValueRef(new TypedValue(result), this);
                            }
                            result.put(entry.getKey(), entry.getValue());
                            lastKey = entry.getKey();
                        }
                    } else {
                        throw new SpelEvaluationException(selectionCriteria.getStartPosition(),
                                SpelMessage.RESULT_OF_SELECTION_CRITERIA_IS_NOT_BOOLEAN);
                    }
                } finally {
                    state.popActiveContextObject();
                    state.exitScope();
                }
            }

            if ((this.variant == FIRST || this.variant == LAST) && result.isEmpty()) {
                return new ValueRef.TypedValueHolderValueRef(new TypedValue(null), this);
            }

            if (this.variant == LAST) {
                Map<Object, Object> resultMap = new HashMap<Object, Object>();
                Object lastValue = result.get(lastKey);
                resultMap.put(lastKey, lastValue);
                return new ValueRef.TypedValueHolderValueRef(new TypedValue(resultMap), this);
            }

            return new ValueRef.TypedValueHolderValueRef(new TypedValue(result), this);
        }

        if (operand instanceof Iterable || ObjectUtils.isArray(operand)) {
            Iterable<?> data = (operand instanceof Iterable ?
                    (Iterable<?>) operand : Arrays.asList(ObjectUtils.toObjectArray(operand)));

            List<Object> result = new ArrayList<Object>();
            int index = 0;
            for (Object element : data) {
                try {
                    state.pushActiveContextObject(new TypedValue(element));
                    state.enterScope("index", index);
                    Object val = selectionCriteria.getValueInternal(state).getValue();
                    if (val instanceof Boolean) {
                        if ((Boolean) val) {
                            if (this.variant == FIRST) {
                                return new ValueRef.TypedValueHolderValueRef(new TypedValue(element), this);
                            }
                            result.add(element);
                        }
                    } else {
                        throw new SpelEvaluationException(selectionCriteria.getStartPosition(),
                                SpelMessage.RESULT_OF_SELECTION_CRITERIA_IS_NOT_BOOLEAN);
                    }
                    index++;
                } finally {
                    state.exitScope();
                    state.popActiveContextObject();
                }
            }

            if ((this.variant == FIRST || this.variant == LAST) && result.isEmpty()) {
                return ValueRef.NullValueRef.INSTANCE;
            }

            if (this.variant == LAST) {
                return new ValueRef.TypedValueHolderValueRef(new TypedValue(result.get(result.size() - 1)), this);
            }

            if (operand instanceof Iterable) {
                return new ValueRef.TypedValueHolderValueRef(new TypedValue(result), this);
            }

            Class<?> elementType = ClassUtils.resolvePrimitiveIfNecessary(
                    op.getTypeDescriptor().getElementTypeDescriptor().getType());
            Object resultArray = Array.newInstance(elementType, result.size());
            System.arraycopy(result.toArray(), 0, resultArray, 0, result.size());
            return new ValueRef.TypedValueHolderValueRef(new TypedValue(resultArray), this);
        }
        if (operand == null) {
            if (this.nullSafe) {
                return ValueRef.NullValueRef.INSTANCE;
            }
            throw new SpelEvaluationException(getStartPosition(), SpelMessage.INVALID_TYPE_FOR_SELECTION, "null");
        }
        throw new SpelEvaluationException(getStartPosition(), SpelMessage.INVALID_TYPE_FOR_SELECTION,
                operand.getClass().getName());
    }

    @Override
    public String toStringAST() {
        StringBuilder sb = new StringBuilder();
        switch (this.variant) {
            case ALL:
                sb.append("?[");
                break;
            case FIRST:
                sb.append("^[");
                break;
            case LAST:
                sb.append("$[");
                break;
        }
        return sb.append(getChild(0).toStringAST()).append("]").toString();
    }

}
